Fat Makes Eggs Tender

Recipes engineered for perfection—what exactly does that mean? The Science series takes you inside the experiments behind 50 cooking concepts featured in our new book, The Science of Good Cooking, by the editors of Cook’s Illustrated.

Scrambled eggs should be a dreamy mound of big, soft, wobbling curds. They should be cooked enough to hold their shape when cut but soft enough to eat with a spoon. An omelet, on the other hand, must be firm enough to roll or fold, but the eggs should still be tender and soft. Unfortunately, all too often BOTH dishes turn out dry, tough, or rubbery. Sometimes this is due to overcooking. But no matter how much you cook the eggs, they need some help to keep them tender. The magic ingredient? Fat.

The Backstory

First, let’s talk about what happens to eggs when you cook them. To understand what’s really happening, you have to start with the notion that eggs actually contain distinct elements—the whites and the yolks—that behave quite differently.

The whites are 88 percent water, 11 percent protein, and 1 percent minerals and carbohydrates. The yolks are 50 percent water, 34 percent lipids, and 16 percent protein. When eggs are heated, the water turns to steam. The protein strands begin to unfold, sticking to each other, and eventually forming a latticed network. The formation of this lattice gel is called coagulation—the transition from liquid to a semisolid that you can pick up with a fork.

Ideally, the denaturing proteins will form a loose network that is capable of holding on to the water in the eggs, which will make the cooked eggs tender and fluffy. But it’s too easy for the proteins to form very tight bonds with each other, squeezing out too much liquid in the process. Here’s where the fat comes in.

Scrambled egg recipes generally call for some sort of dairy like milk. The fat in milk coats the proteins and slows down the coagulation process. The water in the milk provides additional moisture, helping to keep the eggs tender. (The liquid also produces steam, making fluffier and lighter scrambled eggs.)

Omelets are a bit different. An omelet needs enough structure to allow for rolling and folding, but too much will result in rubbery eggs. While scrambled eggs should be fluffy, an omelet is more compact. Therefore, there’s no need for additional liquid. In fact, adding dairy to eggs causes problems when making omelets—the extra liquid prolongs the cooking time and toughens the omelet. Our solution: Small cubes of fat in the form of butter.

The fat in the butter coats the egg proteins and produces an omelet that is set but still tender. At least in theory. When developing the experiments for The Science of Good Cooking, Associate Editor Dan Souza tested the importance of fat when making tender eggs with omelets–a lot of omelets.

The Experiment

Using our Perfect French Omelet recipe, Dan cooked two batches of omelets. For one he used cubed frozen butter. (Frozen butter doesn’t melt as quickly and therefore disperses more evenly throughout the egg.) The other he made without any butter at all.

After cooking them, he rolled all of the omelets up like cigars and placed a 2-pound lead fishing sinker on the middle of each.

The heavy 2-pound weights easily crushed the omelets that contained butter. No surprise there. As the frozen butter cubes melted in the omelets made with butter, the fat prevented the protein strands in the eggs from forming tight bonds. The result was an omelet that held its shape but was still very tender.

On the other hand, the omelet without butter showed only a tiny depression. What gives?

Since the eggs in the butter-less omelet contained little fat to interfere with coagulation, the latticed protein network was able to form tighter bonds. These tighter bonds resulted in a tougher, more resilient omelet—great for supporting a lot of weight, but not for eating.

The takeaway? When it comes to omelets, butter is better.

MAKE IT NOW

Our recipe for Perfect French Omelets is free through November 5, 2012.

Got any eggy questions? Leave 'em in the comments.